Mysterious electrical bursts warn of material collapse
Inexplicable flashes of electricity burst out of powdery materials seconds before they form cracks and fail. If better understood, the flashes could be monitored to forewarn of earthquakes, concrete bridge collapses or failures in the ceramic components of engines, such as turbine blades.
Troy Shinbrot of Rutgers University in Piscataway, New Jersey, and colleagues discovered the flashes by studying small avalanches created in the lab by swirling powders, such as flour, in revolving cylinders.
Electrical charges as large as 500 volts were detected up to 4.5 seconds before the avalanches occurred.
The team found that the bursts originated from tiny flaws in the structure of the densely packed powder. These propagated towards the surface as the cylinder revolved, eventually resulting in a crack that sheared off a portion of the powder from the main body.
It is well known that failing materials, and earthquakes, release electrical signals. What's new, Shinbrot says, is the discovery that the discharges are triggered by structural flaws preceding the failure itself. The researchers saw the same thing in powders used to make pharmaceuticals.
They have no explanation as yet but have ruled out a build-up of static electricity, chemical production of electricity and pressure effects.